1. Field of the Application
The present invention relates to a differential signal pair transmission structure, and more particularly, to a symmetric differential signal pair transmission structure and a wiring board and an electronic module utilizing the same.
2. Description of Related Art
In the semiconductor industry, it has become the tendency of the industry to develop integrated circuit (IC) elements with high integrity and high processing speed. Along with the steady advancements of integrated circuit element efficiency, the transmission frequency of electronic signals in a chip is gradually increased. However, when the frequency of an electronic signal is increased to a high-frequency status, for example, beyond a gigahertz (GHz, i.e. one thousand million hertz), the internal signals of a chip would be easily interfered by noise, so that transmission distortion caused by the noise gets more significantly. Herein crosstalk is considered as one of the most common noise interferences. In fact, crosstalk phenomenon mainly comes from a coupling between two adjacent conductors and thereby results parasitic inductance and parasitic capacitance, and the crosstalk gets more seriously with increasing wiring layout density in the IC elements.
At present, differential signal pair transmission technology is widely used to connect the integrated circuit elements and electrical connectors in high speed applications. The electrical connectors are, for example, Universal Serial Bus 3.0 (USB 3.0), Serial Advanced Technology Attachment (SATA) and Peripheral Component Interconnection Express (PCIE) and the like.
In some situations, the integrated circuit element, for example a chip, and the electrical connector are required to separately assemble on the opposite surfaces of the wiring board. When the differential signal pair paths are used to electrically connect the chip and the electrical connector, the differential signal pair paths have to pass through the wiring board and extend from a surface to the other surface of the wiring board. Since the differential signal pair polarities of the chip and the electrical connector are exactly opposite, one of the signal polarities of the differential signal pair has to detour in the wiring layout. For instance, the length of the negative signal path has to be longer than that of the positive signal path and results the dissymmetry between the two signal paths. Thus, problems of time skew would occur in differential signal pair transmission. And consequently, the high speed transmission efficiency of the differential signal pair paths would be reduced.